Focused Ion Beam Engineering of Carbon Nanotubes for Optical Rectenna Applications

The optical rectenna is a device that converts the optical range of electromagnetic radiations to a direct current. Optical antennas, as for the radio frequency (RF) antennas, require an antenna's structure in the range of optical light EM wavelengths, i.e., a few hundred nanometers to a few micrometers. Herein, we demonstrate the optical rectenna effect of single-wall carbon nanotubes (SWCNTs) by cutting them in the resonance lengths of monopole nano-antennas (i.e., λ/4) of 100, 150, and 200 nm to convert incident red, green, and blue lights into a direct current. The physical engineering (cutting) of SWCNTs dispersed on SiO₂/Si, comparable to one-quarter of the incident monochromatic light wavelength (i.e., red, green, and blue), is carried out with high-energy gallium (Ga) ion beams, with the help of a focused ion beam (FIB) system. The rectenna characteristics of these engineered SWCNTs are investigated using conductive mode atomic force microscopy (C-AFM). This unprecedented approach to investigating the optical rectennas will open more directions to study the rectenna effect at the nanometer scale.